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December 5, 2008
Microbiology notes
1. Terminology
c. Reservoir (for infectious disease): Where organisms that causes a particular disease exists in nature.
d. vector: living organism that can transmit an infectious disease from host to host.
e. Virulent: ability of microbe to cause disease in host
f. virulence factor: any trait ( expressed gene) that a microbe has that contributes to its ability to cause disease.
f. Invasive disease: symptoms are caused by a microbe growing in a normally sterile site.
i. Invasion Factor: any trait which contributes to microbes ability to cause an invasive disease.
h) toxigenic disease: Symptoms caused by microbe in non-sterile site expressing protein that’s toxic to us (exotoxin).
II. Ewald’s hypothesis: In general, not in the interests of a pathogen to cause symptoms in a host.
III. Two examples of invasive bacterial diseases
a. Plague
i. Yersinia pestis- gram negative, grows in our blood and lymph nodes. Grows within immune cells.
ii. Virulence factors:
a. Capsule
b. Produces protein that induces apoptosis in immune cells.
c. Hemagglutinin: clots blood
d. Only produced at 25 ®c
e. Plasminogen activator: Prevents blood clots and makes it easier for blood to flow, Prevents immune cells from going to were bacteria are. Its gene expressed controlled by sigma factor which is produced at 37®c
iii. Fleas and rats- many carry black plague. Gets from rodents to people by rat being bitten by fleas and the fleas bite a person.
1. Blood clot in flea gut perpetual hunger for flea more bites
2. For bacteria to spread, must go throughout blood of host. Should make protein to stop closts spread through bloodstream
3. Pneumonic plague: Person to person airborne spread of disease
b. Scarlet Fever
i. Streptococcus pyogenes- gram positive cocci. Can cause strep throat to scarlet fever. Spreads from respiratory tract  blood leads to patchy rash, high fever, strawberry tongue, blindness, heart problems, death
ii. Virulence factors: capsule, proteins that lyse blood cells
1. Graph shows scarlet fever deaths of 1840-1940. Don’t start using antibiotics until 1941. Decline in symptoms is not due to something we did. When people became sick a prevent of spread was used. People were quarantined and not allowed contact with anyone but maybe doctor and nurse.